This proposal has as its basic theme the study of mammalian phosporylase phosphatase in terms of its enzymology and its regulation. There are three phosphoprotein phosphatase activities which are central to the regulation of mammalian glycogen metabolism: phosphorylase phosphatase, glycogen synthase phosphatase and phosphorylase kinase phosphatase. Present evidence indicates that phosphorylase phosphatase also dephosphorylates glycogen synthase and possibly functions as a multiple dephosphorylating agent in direct analogy with the multiple functions of cAMP dependent protein kinase. Recent evidence from this laboratory has indicated the existence of an inactive form of phosphorylase phosphatase, and also the existence of a protein inhibitor of the enzyme activity. More specifically, the aims of this work are: (1) to extend our knowledge of the basic enzymology of phosphorylase phosphatase; (2) to delineate the mechanisms involved in the regulation of the enzyme, in terms of the mechanism of interconversion of the active and inactive forms; (3) to isolate and characterize the newly discovered inactive form of the enzyme; (4) to isolate and characterize the protein inhibitor of the enzyme; and (5) to examine the effects of hormones on the regulation of the enzyme.